Machines for the forming, filling and sealing of packages made from a continuous web or film of material are well known in the art. Such machines require a smooth and efficient means for advancing the film over the former in cooperation with the other parts of the system to insure that the film is to be properly formed into a tube, filled and then sealed into individual packages.
In order to meet this requirement, film advancing mechanisms usually are built using clamps that engage and move the tube. Typically, the movement is imparted by moving the clamping/sealing jaws, or clamping/rotating feed belts or rollers in engagement with the tube above the sealing jaws. Many packaging machinery users prefer the belt/roller approach, and considerable research and development is proceeding in this direction today. As shown in relatively recent U.S. Pat. Nos. 3,918,235 to Brown, Jr. et al and 3,826,061 to Hunter, the rollers or belts for advancing the film are externally engageable with opposite sides of the film along a hollow mandrel that allows product delivery to the tube. Belts and rollers, however, are not without their disadvantages.
Over an extended period of use, belts may stretch and wear to the extent that they began to slip over the pulleys with which they are associated and driven and/or slip on the packaging film. This slipping deleteriously leads to an uneven film advancing action, or advancing film not of a sufficient length for forming a complete package within the allocated time. Similar problems also arise with the use of rollers where a relatively small surface area on the periphery of each rotating roller contacts the film at any one time to provide the advancing action. With reduced surface area, there is a greater probability of slipping against the film leading to uneven or insufficient film advance.
In an effort to overcome these problems complicated vacuum belt or roller systems have been provided as, for example, in U.S. Pat. No. 4,043,098 to Putman, Jr. et al. In such a system air is drawn through the belt or roller from the surface facing the film. The suction created aids in the clamping of the film so as to prevent slipping and provide consistent and proper film advance.
Despite the improved film advancing action that a vacuum roller belt system provides, there are still disadvantages. The vacuum equipment for drawing air through the belts or rollers greatly increases the initial capital expense of the package forming equipment. Further, additional and costly labor intensive maintenance of the vacuum system is periodically required and the down time associated with this maintenance has an adverse effect of productivity.
Recognizing the disadvantages of advancing a continuous film by the rotating action of endless belts or rollers, the prior art also includes the development of some complicated reciprocating drive means for forming a loop of film as, for example, shown in U.S. Pat. No. 3,762,128 to Persson et al. In Persson, rollers attached to reciprocating swing arms pull a loop of film from the supply reel. The loop of film is then pulled down and advanced over the former by the weight of material filled into the previously formed bag. This two-stage film advancing mechanism fails to provide the positive action necessary for the even, smooth and efficient advancing of film over the tube former. The likelihood of improper tube formation from the continuous film is greatly increased. This, of course, results in unreliable packaging machine performance.
Consequently, a need is identified for a packaging machine having a simple and reliable film advancing mechanism providing smooth and consistent operation without slipping and cooperating with the other components of the machine in a new, more efficient manner.